Temperature compensator for hydraulic systems



S. l. MaCDUFF TEMPERATURE COMPENSATOR FOR HYDRAULIC SYSTEMS May 1, 1951 Filed oct. 18, 1946 N mmwuw.

, /A/ l/ew Tof? W W A3 H.. M .Y

W. N M 7 r A.

Patented May 1, 1951 entre 'ENT GFFICE TEMPERATURE COMPENSATOR FR HYDRAULIC SYSTEMS Application October 18, 1946, Serial No. '704,261

(-Cl. Gil-54.5)

lClaims.

This invention relates to hydraulic systems and more particularly to a device for use in a hydraulic system to compensate the system for temperature changes of the duid therein.

Another object of the invention resides in the provision of a temperature compensating device` for use in a two pipe-line closed hydraulic system wherein a valve member has two independent areas, one of which is subjected to iiuid under pressure in one line and the other of which is subjected to fluid under pressure in the other line whereby a simultaneous increase in pressure in both lines due, for example, to temperature increase will unseat the valve member to allow for the escape of the expanded uid from one of the lines.

A yet further object of the invention resides in the provision of temperature compensating device for use in a two pipe-line closed hydraulic system wherein a valve member has two independent areas, one of which is subjected to fluid under pressure in one line and the other of which is subjected to iiuid under pressure in the other line whereby anV increase in working pressure within a predetermined range in one line only will be ineifective to unseat the valve member but where an increase in pressure in both lines due to temperature variation will unseat said valve member to release fluid from one of the lines.

A more important object of the invention resides in the provision of a two pipe-line closed hydraulic system having a transmitter cylinder and a receiver cylinder1 therein and incorporating a mechanism which compensatesdthe system for change in volume of fluid due to change in temperature and wherein the volumes of the two cylinders are unequal to permit complete difplacement of fluid from one end of one of the cylinders without causing the piston in the other cylinder to move to the end thereof to complete its stroke.

An object of the invention resides in the provision of fluid compensating means for two pipeline closed hydraulic system in which the fluid therein is kept at a predetermined pressure level and wherein a change in the volume of fluid in the system with a consequent pressure change due to temperature variation will be offset by withdrawing or adding fluid to one of the lines of the system.

Figure 1 discloses the temperature compensating mechanism and two pipe-line closed hydraulic system of the invention in diagrammatic form.

Figure 2 is a diagrammatic view illustrating the displacement of the transmitter cylinder piston due to temperature Variation.

Referring now to Figure l of the drawing reference numerals l!) and l2 designate transmitter and receiver cylinder assemblies respectively interconnected by lines le and I5 to provide a two pipe-line closed hydraulic system in which a temperature compensating mechanism I8 is disposed in a manner to maintain fluid in the system at a substantially constant volume irrespective of temperature variation.

The transmitter cylinder assembly or transmitter unit IS comprises a cylinder 2e having a piston 22 therein dividing the cylinder into two chambers, one at each end thereof. The piston 22 has a rack 24 integral therewith. A shaft 25, with gears 28 and 3B secured to opposite ends of the shaft, is carried by the cylinder 2i). A manual controlled member or steering Wheel 32 is splined or otherwise secured to one end of a shaft 3G having a pinion gear 35 suitably fixed thereto at the other end for engagement with the gear 30 to thereby move the piston 22 within the cylinder when the steering wheel is rotated. A conduit or connection 3E connects the ends of the cylinder 20. A bleed or centering valve 31 is located in the connection Se for manually controlling the passage of fluid between the ends of the cylinder 2G for a purpose toA be hereinafter described.

The receiver cylinder assembly l2 comprises a cylinder 33 smaller in volume than cylinder 2!) and having a piston 13E) therein dividing the cylinder into a pair of opposed chambers, A piston rod 'i2 is carried by the piston Ml and extends through the ends of the cylinder to provide equal effective areas on either side of the piston. A conduit or connection M connects the ends of the cylinder 38. A bleed or centering valve 45 is disposed within the connection Mi for manually controlling the passage of fluid between the ends of the cylinder 38 for a purpose to be hereinafter set forth.

The temperature compensating mechanism i8 includes a valve member Il@ seated in passage 55 which communicates line i4 with a reservoir 52 the interior of which is divided by a flexible diaphragm 53 into an upper chamber 54 into which air is forced and a lower chamber E5 in which the passage 5!) terminates to thereby provide for changes in volume of the uid in the system. The upper or air chamber 5S is further divided by a rigid semispherical wall 55 designed to limit upward deflection of the diaphragm so as to prevent it from overexpanding or rupturing. This wall is provided with a hole which permits free passage of air. However', the holc is small enough to prevent extrusion of the diaphragm if it should be forced against the hole by a high pressure. The valve member Q3 has a step 5'3 integral with a head St which is urged into a valve seat 52 by a spring 64 to normally cut off communication between the chamber 56 and the line Hl. The stern of the valve member has one end in communication with line IE5 to thereby subject said one end to the uid pressure in said line. Aseal El cncircles the valve stem 58 to prevent leakage between the lines ifi and l' along the valve stem. It will be noted that the effective annular area of the valve head formed between the valve seat and valve stem and on which the pressure line id acts when the valve member is seated is equal to the effective area of the valve stem 5B on which the pressure in line IS acts. In the present illustration the spring S is selected to exert a force on the valve member equal to substantially onehalf the total operating force required for the system. Actually however, the total force holding the valve member on its seat is the summation of the spring force G4 plus the pressure of the fluid in chamber 56 acting on enlarged head of the stem. It should be pointed out that the force necessary to hold the valve member on its seat may be obtained solely by the pressure in chamber 56. A check valve @E is located in a passage 58 which connects the chamber 55 to line I4 to thereby admit the flow of fluid from the chamber to the line but to prevent flow in the opposite direction. A bleed diversion valve l is located in the line Ill between the points of connection of the passages 5t and 53 with the line. A conduit l2 intersects the passage 68 and is adapted to be connected to a fluid source, such as an accumulator 13. A check valve 'lil is located in the conduit or passage l2 to allow flow in one direction only. A spring 'i6 biases the check valves 66 and M onto their seats. A manual bleed valve 'I8 is disposed in the conduit or passage 'i2 to normally close the system to the source. Another manual bleed valve Si! is disposed in a conduit 82 adapted to connect line It to a main systern reservoir 84.

As hereinbefore pointed out the reservoir 52 is divided into two chambers 5&5 and 5G. Chamber 54 is provided with a check valve 8% adapted to be connected to an air pressure source for putting the chamber under air pressure. When air is forced into chamber' 55. before chamber 55 is filled with oil the diaphragm 53 assumes a position shown in dotted lines, Figure 2.

To make the two pipe-line closed hydraulic system ready for putting fluid therein under pressure and for subsequently lling the same the bleed or centering valves T8, 8D, 3l and d6 are opened and valve 'lil closed to permit free circulation of fluid to purge the system Aof air or the like. Fluid can now flow freely through valve T8 past the check valve lil into the right end of line I4 which connects the temperature compensating mechanism I8 to one end of the receiver cylinder I2, from here the fluid is allowed to iiow around to the other end through bleed valve 45, then through line I5 to one end of the transmitter cylinder, from which the duid is allowed to pass through bleed valve 3'! to the other end of the transmitter cylinder and thence to the reservoir past valve 80. After allowing the fluid to circulate a short time to insure removal of all air from the system valve Si! is closed and valve 'Ill opened, as shown, whereupon the fluid ceases to circulate. After closing valve 86 fluid in the system is put under pressure since valve I8 is still open. As soon as the pressure in the closed system rises to a predetermined value depending on the force necessary to move the valve member 48 from its seat fluid will pass into chamber 5 to thereby deflect the diaphragm from its dotted line position until it is pressed tightly against the wall 55. With the system now bled and completely filled the valve 'i8 is closed. Now, by opening or rather loosening any of the several tube joints in the system a measured quantity of oil may be bled from the system leaving the diaphragm substantially as shown in full lines, so that there is now room both for expansion and contraction of fluid. The measured quantity of fluid removed is preferably varied in accordance with the ambient temperature so that the diaphragm will occupy a certain position at some standard temperature such as '70 F. Before closing the bleed or centering valves 31 and Q6, pistons 22 and d respectively should be centered in their respective cylinders. Leaving valves 3'." and ll open allows for the free flow of fluid from one end of the cylinders to the other ends thereof when centering the pistons as aforementioned. After this has been done the valves are closed and the system is now ready for use.

Figure 2 is a diagrammatic representation of the system of Figure l illustrating the extreme positions to which the pistons of the transmittel' and receiver cylinders may move due to temperature variation of the fluid. The difference in volumes is made such that if a loss in velu.A e of fluid from one of the lines equal to the shrinkage of the iiuid at the lowest temperatures to which the system is designed occurs, the transmitter' cylinder still will have sufficient fluid therein to operate the piston in the receiver cylinder through its full stroke. In designing the system maximum and minimum temperature variations under which the system will operate must be determined at the outset. The arrangement is such that under an ambient temperature of 70 F. the transmitter and receiver cylinder pistons and diaphragm 53 will be in the position shown in solid lines. If the temperature should drop to say 40 F. the fluid in the lines Ill and 5 will shrink. The transmitter cylinder piston will have moved to the position shown in dot dash lines and the receiver cylinder piston will remain in its center position since it is held from moving by a load attached thereto, shown. At the same time diaphragm 53 will have been moved by the pressure in chamber 5 to the position shown in dot and dash lines. The volume A cf fluid remaining in the transmitter cylinder' is still sufficient to displace piston 4i) of the receiver cylinder to the right to the Aend of its stroke. On the other hand if the temperature should rise tc say F. the fluid in lines I4 and l@ will expand. Due to the expansion of iluid in line i5 piston 22 will have moved to the position shown dotta-il. lines with piston remaining because of its fixed load, not shown. Expansion of the fluid in line I I and movement of piston 22 has caused diaphragm 53 to assume the position shown in dotted lines. The Volume of fluid B in the transmitter cylinder is still suflicient to displace the receiver cylinder piston 40 to the left its full stroke. Thus it will be seen that transmitter cylinder must have a total displacement equal to the displacement of the receiver cylinder plus the total expansion of the liuid in one line from the minimum to maximum temperature. The fluid chamber 56 must have a volume at least equalv to twice the total expansion of the fluid in one' line, or in other words the total expansion in both lines. Both the transmitter cylinder and chamber 56 may have a further additional volume to permit slight leakages to occur without requiring immediate re-centering and refilling.

Operation of the temperature compensating mechanism is as follows:

With the pistons of the transmitter and receiver cylinders of the system in the positions shown in the drawing, assume an increase in ambient temperature of the receiver cylinder. This will cause the fluid in the ends of the receiver cylinder and the two-pipe lines i4 and I6 to expand until the pressure in theclosed system has risen to a predetermined value, depending upon the summation of the force of spring 6,4 and the pressure of the uid acting in chamber 56, at which time valve member 48 will be unseated to allow the escape of fluid from line i4 to chamber 56 to thereby maintain the system pressure at a ixed maximum value. It will be noted that the fluid under pressure in both lines acts on the valve member tending to unseat the same 'when the increase in pressure in the pipe-lines is due to temperature increase. Since the pressure developed due to an increase in temperature of the uid acts on an area twice that of the working pressure, the rst mentioned pressure, per unit area, must be only one-half as great as the working pressure to unseat the valve.

If we assume a decrease in ambient temperature of the receiver cylinder the pressure of the fluid in the ends of the receiver cylinder and the two pipe-lines will drop, thus decreasing the total force acting on check valve 66. After the pressure of the uid in the system has dropped a predetermined amount depending upon the pressure of the fluid in chamber 56 the check valve will open to admit fluid to line I4 to replenish the same.

If it is desired to move piston 130 to the right for example, steering wheel 32 is rotated in a direction to cause piston 22 to move to the right.`

Movement of piston 22 to the right as aforementioned will increase the working pressure of the fluid in pipe-line i4 and decrease the pressure of the fluid in pipe-line I5. The working pressure of the fluid in pipe-line l due to operation of the steering wheel can rise to a value twice that of the maximum fluid pressure in the two pipe-lines caused by au increase temperature. rhis is because the uid under pressure in pipeline I4, created by movement of piston 22, is acting on only one-half the effective area of the valve member in a direction vtending to unseat the same against spring 64. The fluid pressure acts only on the annular area of the valve member located between the valve seat and stem 58 and subjected to the pressure of the fluid in line I4. Rotation of' the steering wheel in the direction to cause piston all to move to the left will increase the working pressure of the fluid in pipeline I6 and decrease the pressure of the iiuid in pipe-line i4. Here, as described above the fluid under pressure in line l5 acts only on one-half the effective area of valve member Q8 tending to unseat the same, However, at this time the fluid under pressure acts on the end of the valve stem which is subjected to the pressure in line I6 instead of on the annular area. As hereinbefore pointed out the area of the end of valve stem 58 is equal to the annular area of the valve member located between the valve seat and the valve stem.

The chamber 55 is preferably made larger than necessary for full temperature compensation in order to provide a quantity of fluid to make up for leakage at the various glands and joints of the system. If such leakage takes place in pipe I6 the transmitter piston 22 may be moved substantially off center. This may be corrected by opening valve 31, moving steering wheel 32, and reclosing the valve.

Although the follow-up system and temperature compensating mechanism of this invention have been described in connection with certain specific embodiments, the principles are susceptible of numerous other applications that will readily occur to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described the various features of the invention, what I claim as new and desire to secure by Letters Patent is:

I claim:

l. The combination with a two pipe-line closed hydraulic system, of a mechanism for compensating for change in volume of fluid in the system due to temperature variation comprising a reservoir for fluid, a passage connecting one of the two pipe-lines to the reservoir, a valve seat in the passage, and a valve member normally` urged toward said seat, said valve member constructed and arranged to have two equal areas, one of the areas being subjected to fluid under pressure in one of the pipe-lines and the other of the areas being subjected to fluid under pressure in the other of the pipe-lines and acting in a direction on the valve member tending to unseat the same, whereby an increase in volume of fluid above a predetermined value in the two pipe-lines of the system due to an increase in temperature will cause the valve member to unseat to allow liuid to escape to the reservoir.

2. The combination with a two pipe-line closed hydraulic system, of a mechanism for compensating for change in volume of fluid in the system due to temperature variation comprising a reservoir for fluid, a passage connecting one of the two pipe-lines to the reservoir, and a valve normally seated to close said passage, said valve constructed and arranged to have two equal areas subjected to iiuid under pressure from the two pipe-lines to unseat said valve to open said passage to discharge fluid into the reservoir should the volume of fluid in the system and consequently the pressure, increase beyond a predetermined value due to an increase in temperature of the fluid.

3. The combination with a two pipe-line closed hydraulic system, of a mechanism for compensating for change in volume of iluid in the system due to temperature variation comprising a reservoir for fluid, a passage connecting one of the two pipe-lines to the reservoir, and a valve normally spring seated to cut ou the flow between the reservoir and said one of the two pipe-lines, said valve constructed and arranged so that an increase in working pressure in the system acts only on a fraction of the total effective area ci the valve tending to unseat the same, whereby the force created due to the working pressure of the fluid in one only of the two pipe-lines can be made to equal the total force normally urging the valve onto its seat, and the pressure in the system due to increase in temperature of the fluid acts in the two pipe-lines and on the total-effective area of the valve in a direction tending to unseat the same, whereby the force created due to 'said pressure in each of the two pipe-lines caused by an increase in the temperature can be only a fractional part of the total force normally urging the valve onto its seat.

4. The combination with a two pipe-line closed hydraulic system, of a mechanism for compensating for change in volume of iluid in the system due to temperature variation comprising a reservoir for lluid, a passage connecting one of the two pipe-lines to the reservoir, a valve normally spring seated to cut off the flow between the reservoir and said one of the two pipe-lines, said valve constructed and arranged so that an increase in working pressure in the system acts only on a fraction of the total elective area of the valve tending to unseat the same, whereby the force created due to the working pressure of the fluid in one only of the two pipe-lines can be made to equal the tota-l force normally urging the valve onto its seat, and the pressure in the system due to increase in temperature of the fluid acts in the two pipe-lines and on the total efective area of the valve in a direction tending to unseat the same, whereby the said pressure in each of the two pipe-lines caused by an increase in the temperature can be only one-half of the normal working pressure to thereby produce a force equal to the total force normally urging the valve onto its seat, a second passage connecting said one of the two pipelines to the reservoir, and a valve in the second passage normally closed and arranged therein to open to communicate said one of the two pipe-lines with the reservoir when the volume of fluid in the system falls below a predetermined value due to decrease in temperature of the fluid.

5. The combination with a closed hydraulic system, of a transmitter cylinder, a receiver cylinder, a piston in each cylinder, two parallel pipe lines interconnecting the ends of the transmitter and receiver cylinders, the volumes of the cylinders being imequal so that a change in volume of fluid in one of the pipe-lines due to temperature variation will not aiect the volume of fluid in the transmitter cylinder to the extent that the remaining volume will not be adequate to cause complete displacement of the piston in the smaller cylinder, and a mechanism for compensating for f change in volume of fluid in the syst in due to temperature variation comprising a reservoir for fluid, two parallel passages connecting one of the two pipe-lines to the reservoir, a valve in each passage, one of said valves constructed and arranged to respond to a decrease in Volume of fluid in the system below a predetermined value due to a decrease in temperature to thereby communicate the system with the reservoir, the other of said valves constructed and arranged to have two equal arcas subjected to fluid under pressure from the two pipe-lines to unseat said valve to open said passage to discharge fluid into the reservoir should the volume of uid in the system and consequently the pressure, increase beyond a predetermined value due to an increase in temperature of the uid.

6. A valve mechanism adapted to be connected between a reservoir for fluid and a two pipe-line closed hydraulic system, comprising a passage adapted to have its ends connected to the reservoir and to one of the two pipe-lines, a valve seat in the passage, and a valve member normally urged toward the seat, said valve member constructed and arranged to have two equal areas, one of the areas being subjected to line pressure in one of the two pipe-lines and the other of the areas being subjected to line pressure in the other of the two pipe-lines, whereby said valve member will be unaffected by working pressure within one of the two pipe-lines up to a predetermined value but will be unseated by a second pressure slightly in excess of one-half said predetermined working pressure and caused by an increase in temperature of the uid in each of the two pipe-lines and acting on the two equal areas.

7. A valve mechanism adapted to be connected between a reservoir for fluid and a two pipe-line closed hydraulic system, comprising a passage adapted to have its ends connected to the reservoir and to one of the two pipe-lines, a valve seat in the passage, a valve member normally urged toward the seat, said valve member constructed and arranged to have two equal areas, one of the areas being subjected to line pressure in one cf the two pipe-lines and the other of the areas being subjected to line pressure in the other of the two pipe-lines, whereby saidlvalve member will be unaffected by working pressure within one of the two pipe-lines up to a predetermined value but will be unseated by a second pressure slightly in excess of one-half said predetermined working pressure and caused by an increase in temperature of the huid in each of the two pipe-lines and acting on the two equal areas, a second passage adapted to have its ends connected to the reservoir and to said one of the two pipe-lines, and a valve in the second passage normally seated and responsive to a preselected minimum pressure caused by a decrease in temperature of the lluid within said one pipe-line to thereby unseat said valve.

8. A mechanism adapted to be connected to a two pipe-line closed hydraulic system and to a fluid reservoir for compensating for change in pressure and volume of fluid due to temperature variation and unaffected by working pressure 1n the system within a predetermined upper limit, comprising a Valve interposed between the reservoir and said two pipe-line system to control iiow therebetween, said valve normally urged toward closed position by a substantially constant force acting on one side thereof and provided with two equal areas on the other side thereof, one of which is subjected to pressure in one pipeline and the other of which is subjected to pressure in the other pipe-line to thereby cause said valve to be urged toward open position, said valve constituted so that the working pressure required per unit area above said predetermined upper limit to open said valve as against the pressure required per unit area to open said valve due to increase in volume caused by increase in temperature will be in a ratio of approximately two to one.

9. A mechanism adapted to be connected to a two pipe-line closed hydraulic system and to a fluid reservoir for compensating for change in pressure and volume of iluid due to temperature Variation and unaffected by working pressure in the system within a predetermined upper limit, comprising a valve interposed between the reservoir and said two pipe-line system to control flow therebetween, said valve normally urged toward closed position by a substantially constant force acting on one side thereof and provided with two equal areas on the other side thereof, one of which is subjected to pressure in one pipe-line and the other of which is subjected to pressure in the other pipe-,line to thereby cause said valve to be urged toward open position, said valve conu stituted so that the working pressure required per unit area above said predetermined upper limit to open said valve as against the pressure required per unit area to open said valve due to increase in volume caused by increase in temperature will be in a ratio of approximately two to one, and a second valve interposed between the reservoir and one of the pipe-lines of said two pipe-line system, said second valve normally urged toward closed position yby pressure in said one of the pipe-lines and urged toward open position by pressure in the reservoir, whereby said one pipeline is replenished with fluid when the pressure therein falls below a predetermined value.

10. The combination with a two pipe-line closed hydraulic system of a device for compensating for changes in volume of fluid in the system due to changes in temperature comprising a reservoir, means for maintaining fluid in the reservoir under a predetermined pressure, a relief valve connecting one of said pipe lines to said reservoir and having an area subjected to fluid pressure in said pipe-line and having another area subjected to fluid pressure in said other pipe-line, the lluid pressure acting on both of said areas in a direction tending to open said relief valve, said relief valve being set to open when the pressure in both of said lines is in excess of reservoir pressure, or when the pressure is greater in the ratio of said areas in said one line only.

ll. The combination with a two pipe-line closed hydraulic system of a device for compensating for changes in volume of i'iuid in the system due to changes in temperature comprising a reservoir, ineans for maintaining fluid in the reservoir under a predetermined pressure, a relief valve connecting one of said pipe-lines to said reservoir and having an area subjected to fluid pressure in said pipe-line and having another area subjected to fluid pressure in said other pipe-line, the fluid pressure acting on both of said areas in a direction tending to open said relief valve, said relief valve being set to open when the pressure in both of said lines is in excess of reservoir pressure, or when the pressure is greater in the ratio of said areas in said one line only, and a check Valve opening from said reservoir to said one line.

12. The combination with a two pipe-line closed hydraulic system of a device for compensating for changes in volume of fluid in the system due to changes in temperature comprising a source of uuid under a predetermined pressure, a relief valve connecting one of said pipelines to said source and having an area subjected to fluid pressure in said pipe-line and having another area subjected to fluid pressure in said other pipe-line, the fluid pressure acting on both of said areas in a direction tending to open said relief valve, said relief valve being set to open when the pressure in both of said lines is in eX- cess of the pressure of said source or when the pressure is greater in the ratio of said areas in said one line only.

13. The combination with a two pipe-line closed hydraulic system of a device for compensating for changes in volume of fluid in the systeni due to changes in temperature comprising a source of iiuid under a predetermined pressure, a relief valve connecting one of said pipe-lines to said source and having an area subjected to pressure in said pipe-line and having another area subjected to fluid pressure in said other pipe-line, the fluid pressure acting on both of said areas in a direction tending to open said relief valve, the fluid pressure from said source acting on said relief valve in a direction tending to ,close the same, said relief valve being set to open when the pressure in both of said lines is in excess of the pressure of said source, or when pressure is greater in the ratio of said areas in one line only, and a check valve opening from said source to said one line,

14. A temperature compensating device for use in a two pipe-line closed hydraulic system cornprising a fluid reservoir under a predetermined pressure, and valve means for controlling ow between said reservoir and one of said pipe-lines, said valve means normally closed and operable in response to the pressure in each of said two pipelines when the pressure in each pipe-line is in excess of the aforesaid predetermined pressure to transfo uid from said one pipe-line to said reservoir, said valve means openable when the pressure in said one of the pipe-lines diminishes beyond the aforesaid predetermined pressure to transfer uid from said reservoir to said one pipeline.

15. A temperature compensating device for use in a two pipe-line closed hydraulic system comprising a fluid reservoir under a predetermined pressure, valve means for controlling ow between said reservoir and one of said pipelines, said valve means including a rst valve normally urged toward closed position by said predetermined pressure and acted upon by pressure in each of said two pipe-lines tending to open the Valve, and a second valve normally urged toward closed position by pressure in said one pipe-line and acted upon by said predetermined pressure tending to open said second valve.

STANLEY I. MACDUFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 568,736 Brown Oct. 6, 1896 568,737 Brown Oct. 6, 1896 2,196,930 Loweke Apr. 9, 1940 2,205,046 Nardone June 18, 1940 2,410,978 Kelly Nov. 12, 1946 

